1. Field of the Invention
The present invention relates to a lightwave distance measuring apparatus which measures the distance to an object to be measured by using pulsed light; and, in particular, to a lightwave distance measuring apparatus which prevents erroneous measurement from occurring due to stray light or the like generated along with transmission of pulsed light.
2. Related Background Art
As the configuration of distance measuring apparatus using lightwaves, biaxial type and coaxial type have conventionally been known from the viewpoint of relative arrangement between the light-transmitting optical path and light-receiving optical path. Of these types, the coaxial type optical system has an advantage in its capabilities of making the apparatus smaller, avoiding parallax, and installing a collimation optical system for targeting the light-transmitting optical path at the object to be measured. Namely, it is a coaxial light-transmitting/receiving type optical system in which the light-transmitting axis of the lightwave used for distance measurement and the light-receiving axis for receiving the reflected light from the object to be measured coincide with each other.
On the other hand, the distance measuring system of the distance measuring apparatus using lightwaves is broadly divided into a continuously modulated wave type in which an LED or semiconductor laser is used as its light source; and a pulse type in which a semiconductor laser, adapted to be pulse-driven, outputting pulsed light with a large peak power is used as its light source. For these distance measuring apparatus, there has conventionally been a demand for enhancing their maximum distance measuring range, and there has been an increasing demand for their measuring capacity in a non-prism configuration which does not employ a reflector such as cube corner prism at the measuring point in order to save the labor and improve the efficiency of operations. For responding to these demands, the pulse type, which can use a large peak power, is definitely advantageous.